During the manufacture of two-piece aluminum containers, e.g., beverage cans, liquid coolant is continuously circulated to cool the forming members and carry off unwanted waste aluminum particles. For economical reasons, the coolant is recirculated through the forming machines for reuse. The recirculated coolant, however, must be filtered to remove the waste aluminum particles. A typical plant manufacturing such aluminum containers may employ twenty forming machines, with a combined coolant requirement of five thousand gallons. It will be readily appreciated that the filtering requirements for five thousand gallons of continuously flowing coolant will be both critical and substantial.
Filter media used to collect aluminum particulate out of a coolant flow have heretofore been either of a high efficiency type or a long life type. The high efficiency type are characterized by collecting a large quantity of particulate out of the coolant flow. This is accomplished by using very small diameter pore openings in the filter media so that very small particulate can be collected out of the coolant flow. The high efficiency type filters, however, are prone to rapid congestion, and hence must be frequently changed. Also, there is a relatively high pressure drop across these prior art high efficiency filters. Therefore, the high efficiency type filters must be frequently changed, thus expensive to use, and do not allow for fast filtration as evidenced by the large pressure drop but provide excellent particulate filtration.
The long life type filters, on the other hand, do not rapidly congest with particulate and are therefore less costly to operate because of the relatively infrequent changing required. This is accomplished by providing larger diameter pore opening in the filter media so that only the larger aluminum particles are collected. The trade-off being, however, that the long life filters can not collect relatively small sized particulate out of the fluid flow due to the relatively large pore openings. Thus, the recirculated coolant is not cleaned as well with the long life type filters when compared with the high efficiency filters, resulting in accelerated wear of the forming machines.
There is a great need in this art for a filter media which both removes very small particulate out of the fluid flow and also possess long life properties to withstand rapid clogging.
U.S. Pat. No. 4,157,968 to Kronsbein, issued June 12, 1979, discloses a tubular filter including a binder-free glass microfiber fleece sandwiched between two layers of a nylon based reinforcing material. The Kronsbein filter media is not self-supporting, but requires two supporting shells made of a stainless steel wire mesh. The steel wire mesh creates an expensive and heavy filter media which would be difficult to properly employ in the manufacture of aluminum containers.
Certain prior art automotive filter media is fabricated from a mixture of cellulose and glass microfibers. This composite material filter media is then supported by a rigid exostructure.